Without limiting the scope of the invention, its background is described in connection with antigen presentation.
Dendritic Cells play a pivotal role in controlling the interface of innate and acquired immunity by providing soluble and intercellular signals, followed by recognition of pathogens. These functions of DCs are largely dependent on the expression of specialized surface receptors, ‘pattern recognition receptors’ (PRRs), represented, most notably, by toll-like receptors (TLRs) and C-type lectins or lectin-like receptors (LLRs) (1-3).
In the current paradigm, a major role of TLRs is to alert DCs to produce interleukin 12 (IL-12) and other inflammatory cytokines for initiating immune responses. C-type LLRs operate as constituents of the powerful antigen capture and uptake mechanism of macrophages and DCs (1). Compared to TLRs, however, LLRs might have broader ranges of biological functions that include cell migrations (4), intercellular interactions (5). These multiple functions of LLRs might be due to the facts that LLRs, unlike TLRs, can recognize both self and nonself. However, the complexity of LLRs, including the redundancy of a number of LLRs expressed in immune cells, has been one of the major obstacles to understand the detailed functions of individual LLRs. In addition, natural ligands for most of these receptors remain unidentified. Nonetheless, evidence from recent studies suggests that LLRs, in collaboration with TLRs, may contribute to the activation of immune cells during microbial infections (6-14).
Valladeau et al. (The Journal of Immunology, 2001, 167: 5767-5774) described a novel LLR receptor on immature human Dendritic Cells related to hepatic Asialoglycoprotein Receptor and demonstrated that it efficiently mediated endocytosis. DC-ASGPR mRNA was observed predominantly in immune tissues—in DC and granulocytes, but not in T, B, or NK cells, or monocytes. DC-ASGPR species were restricted to the CD 14-derived DC obtained from CD34-derived progenitors, while absent from the CD1a-derived subset. Both monocyte-derived DC and tonsillar interstitial-type DC expressed DC-ASGPR protein, while Langerhans-type cells did not. Furthermore, DC-ASGPR was a feature of immaturity, as expression was lost upon CD40 activation. In agreement with the presence of tyrosine-based and dileucine motifs in the intracytoplasmic domain, mAb against DC-ASGPR was rapidly internalized by DC at 37° C. Finally, intracellular DC-ASGPR was localized to early endosomes, suggesting that the receptor recycles to the cell surface following internalization of ligand. These findings identified DC-ASGPR/human macrophage lectin as a feature of immature DC, and as another lectin important for the specialized Ag-capture function of DC.